Abstract

We conducted laboratory experiments where different types of predators were allowed to prey on noxious versus non-noxious tadpoles. The introduced fish Perccottus glenii showed prey selectivity: while actively consuming all seized tadpoles of Rana arvalis and Rana temporaria, it consumed significantly fewer Bufo bufo tadpoles. When a Bufo tadpole was seized, it was frequently rejected after intraoral testing without much damage done to the tadpole. Nymphs of the dragonfly Aeschna cyanea, chewing captured prey, also consumed significantly more tadpoles of Rana spp. than Bufo. Seized Bufo tadpoles were as a rule released seriously damaged. Then Aeschna readily caught the next Bufo tadpole. On the contrary, larvae of the diving beetle Dytiscus marginalis, who suck out their prey, did not reject Bufo tadpoles. Hence, the relative unpalatability of the Bufo tadpoles may provide them with a satisfactory defence against Perccottus, an incomplete defence against Aeschna, and no protection against Dytiscus. It is possible that the relative unpalatability of Bufo tadpoles increases their population mortality in ponds with high Aeschna density.